Hi and welcome,
I can only offer my opinion based on two different e-cigs. I purchased the Joye 510 when I started (only a month ago). The battery life for me lasted 5-6 hours then I would have to switch. I was getting a little frustrated in having to change the batteries 2 or 3 times a day depending on how much I used it. I decided to purchase the eGo because of it's longer battery life and it just looked cooler. I'm such a sucker for anything shiny . Anyhow, I did my initial charge on the eGo battery and used it that same night. I can't speak to everyone's experience with the eGo battery but I used the same battery for almost 18 hours! What I mean by this is that I started using the battery around 6 at night,took it to work, came home, stayed up till 1 am, went to bed, woke up at 7 am and it finally lost charge at 11 am on Saturday morning. Mind you I was NOT casually using it. I don't think I have put it down in 3 days.
That is my experience so hopefully it helps you make a decision. I my eGo.